Plant Communities, Species Diversity, Seedling Bank and

Plant Communities, Species Diversity, Seedling Bank and Resprouting in Nandi Forests, Kenya

Dissertation Zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaft Fachbereich 3: Mathematik/Naturwissenschaften Universität Koblenz-Landau

Vorgelegt am 16. September 2011 von Adane Girma Gebreselasse geb. am 27 Oktober 1974 in Äthiopien

Referent: Prof. Dr. Eberhard Fischer Korreferent: Prof. Dr. Wilhelm Barthlott

This work is dedicated To my father Ato Girma Gebreselass (1937-2004) My mother Woizero Yeshi Kidanewold My wife Enat Ashine My brothers and sisters and To all Ethiopian peasants who did not enjoy formal education but toiled hard to send their children to school hoping that their offsprings will be better off.

Table of Contents List of Tables .......................................................................................................................... VI List of Figures ....................................................................................................................... VIII Abstract ..................................................................................................................................... X 1. General Introduction ...............................................................................................................1 1.1 Tropical Rain Forest .............................................................................................................1 1.2 Biodiversity ..........................................................................................................................3 1.2.1 Species diversity ................................................................................................................4 1.2.2 Species richness .................................................................................................................5 1.3 Deforestation and Fragmentation of Tropical Forests ............................................................6 1.3.1 Deforestation .....................................................................................................................6 1.3.2 Fragmentation ....................................................................................................................8 1.4 Natural regeneration ...........................................................................................................10 1.4.1 Factors affecting seedling regeneration ............................................................................11 1.4.2 Factors affecting regeneration from stump .......................................................................13 1.5. Objective of the study ........................................................................................................14 2. Materials and Methods .........................................................................................................16 2.1 Study Area .......................................................................................................................... 16 2.1.1 Location and physiography .............................................................................................. 16 2.1.2 Geology and soil ..............................................................................................................17 2.1.3 Climate ............................................................................................................................ 18 2.1.4 Vegetation and fauna .......................................................................................................19 2.1.5 Gazettment detail and administration ...............................................................................21 2.2 Data Collection ................................................................................................................... 23 2.2.1 Vegetation data ................................................................................................................23 2.2.2 Environmental data ..........................................................................................................25 3. Floristic Composition of Nandi Forest .................................................................................. 26 3.1 Introduction ........................................................................................................................ 26 3.2 Material and Methods .........................................................................................................27 3.2.1 Study sites ....................................................................................................................... 27 3.2.2 Vegetation sampling ........................................................................................................27 3.2.3 Diversity analysis ............................................................................................................27 3.2.4 Cluster analysis ................................................................................................................34 3.2.5 Ordination ....................................................................................................................... 36 3.3 Results ................................................................................................................................ 38 3.3.1 Floristic composition .......................................................................................................38 III

3.3.2 Alpha and beta diversity ..................................................................................................40 3.3.3 Species accumulation curve ............................................................................................. 42 3.3.4 Species richness estimation .............................................................................................. 43 3.3.5 Floristic similarities .........................................................................................................44 3.3.6 Plant communities ...........................................................................................................44 3.3.7 Ordination ....................................................................................................................... 50 3.4 Discussion .......................................................................................................................... 52 3.4.1. Floristic composition ......................................................................................................52 3.4.2 Alpha and beta diversity ..................................................................................................54 3.4.3 Species accumulation curve and species richness estimation ............................................56 3.4.4 Plant communities ...........................................................................................................58 3.4.5 Description of east African mountain forests ....................................................................61 4. Population Structure of Nandi Forest .................................................................................... 63 4.1 Introduction ........................................................................................................................ 63 4.2 Material and Methods .........................................................................................................64 4.2.1 Study sites ....................................................................................................................... 64 4.2.2 Data collection and analysis ............................................................................................. 64 4.3 Results ................................................................................................................................ 66 4.3.1 Growth forms .................................................................................................................. 66 4.3.2 Height class distribution...................................................................................................67 4.3.3 Diameter class distribution ............................................................................................... 68 4.3.4 Basal area and abundance ................................................................................................ 72 4.4 Discussion .......................................................................................................................... 75 5. Seedling Bank and Resprouting in Nandi Forests ..................................................................79 5.1 Introduction ........................................................................................................................ 79 5.2 Material and Methods .........................................................................................................80 5.2.1 Study sites ....................................................................................................................... 80 5.2.2 Data collection and analysis ............................................................................................. 80 5.3 Results ................................................................................................................................ 82 5.3.1 Seedling bank .................................................................................................................. 82 5.3.2 Regeneration from stumps ............................................................................................... 94 5.4. Discussion ....................................................................................................................... 105 6 Human Impact on Vascular Plant Diversity, Population Structure, Seedling Bank and Resprouting of South Nandi Forest ......................................................................................... 112 6.1 Introduction ...................................................................................................................... 112 6.2 Materials and Methods...................................................................................................... 113 6.2.1 Study sites ..................................................................................................................... 113 6.2.2 Data collection and analysis ........................................................................................... 113 IV

6.3 Results .............................................................................................................................. 116 6.3.1 Floristic composition ..................................................................................................... 116 6.3.2 Alpha and beta diversity ................................................................................................ 117 6.3.3 Population structure ....................................................................................................... 120 6.3.4 Natural regeneration ...................................................................................................... 129 6.4 Discussion ........................................................................................................................ 135 6.4.1 Floristic composition ..................................................................................................... 135 6.4.2 Population structure ....................................................................................................... 136 6.4.3 Seedling bank and resprouting ....................................................................................... 138 7. Conclusion and Recommendations ..................................................................................... 141 References .............................................................................................................................. 145 Appendix ................................................................................................................................ 162 Acknowledgements ................................................................................................................ 170

V

List of Tables Table 1 Area and gazettment details of North Nandi Forest ...................................................... 22 Table 2 Area and gazettment details of South Nandi Forest ...................................................... 22 Table 3 Top ten species rich families recorded in Nandi Forests ...............................................39 Table 4 Families with five or more species in North and South Nandi Forest ............................ 40 Table 5 Various diversity parameters calculated in North and South Nandi Forest .................... 41 Table 6 Number of samples, individuals, observed species and estimated species richness (based on different methods) of Nandi Forests ..................................................................................... 43 Table 7 Number of samples, individuals, observed species and estimated species richness (based on different methods) of North and South Nandi Forest ............................................................ 44 Table 8 Incidence and abundance based similarity indices of North and South Nandi Forests ...44 Table 9 Indicator values of species for the identified plant community of Nandi Forests. ..........48 Table 10 Eigenvalues of the first four axes of DCA and the amount of variance explained by each axes in two Nandi Forests .................................................................................................51 Table 11 Classification (zonation) of esat African mountain forests by different authors...........62 Table 12 Density of woody plants in Nandi Forests of Kenya ................................................... 73 Table 13 Importance Value (IV) of the top 15 common woody plant species in Nandi Forests.74 Table 14. Families represented by four or more species in the seedling population of South and North Nandi Forests .................................................................................................................82 Table 15 List of species with their seedling densities and frequency at the North and South Nandi Forests ........................................................................................................................... 85 Table 16 Different diversity characterstics of seedlings in North and South Nandi Forests........90 Table 17 Incidence and abundance based similarity indices of North and South Nandi Forests .91 Table 18 Incidence and abundance based similarity indices of trees and tree species seedlings in North and South Nandi Forests .................................................................................................92 Table 19 Eigenvalues of the first four axes of DCA and the amount of variance explained by each axes in two Nandi Forests .................................................................................................93 Table 20 Mean number of stumps per plot (400 m2 ) and hectare in South Nandi and North Nandi Forests .....................................................................................................................................95 Table 21 Stumps recorded in Nandi Forests with their resprouting percentage .......................... 96 Table 22 Mean number of sprout (shoot) per stump for species that have ten or more stumps in Nandi Forests ........................................................................................................................... 99 Table 23 Toal number of stumps and number of sprouted stumps in Nandi Forests in each stump diameter class ......................................................................................................................... 100 VI

Table 24 Number of stumps in each stump height class with their sprouting ability and mean number of sprouts per stumps for woody species that have more than 30 stumps .................... 104 Table 25 The first ten species rich families at Kobujoi and Bonjoge ...................................... 117 Table 26 Various diversity parameters calculated at Kobujoi and Bonjoge ............................. 118 Table 27. Number of samples, individuals, observed species and estimated species richness (based on different methods) at Kobujoi and Bonjoge of South Nandi Forest .......................... 120 Table 28 Incidence and abundance based similarity between Kobujoi and Bonjoge ................ 120 Table 29 Density of woody plants at Kobujoi and Bonjoge (South Nandi forest) .................... 127 Table 30 Importance Value (IV) of the top 15 common woody plant species at Kobujoi and Bonjoge of South Nandi Forest ............................................................................................... 128 Table 31 Families represented by three or more species in the seedling population at Kobujoi and Bonjoge .......................................................................................................................... 130 Table 32 Different diversity characterstics of seedlings at Kobujoi and Bonjoge .................... 132 Table 33 Incidence and abundance based similarity indices of seedlings at Kobujoi and Bonjog in South Nandi Forest ............................................................................................................ 132 Table 34 Incidence and abundance based similarity indices of trees and tree species seedlings at Kobujoi and Bonjoge ............................................................................................................. 133 Table 35 Mean number of stumps per plot and hectare at Kobujoi and Bonjoge in South Nandi Forest .................................................................................................................................... 133 Table 36 Species with ten or more stumps at Kobujoi and Bonjoge with their resprouting percentage .............................................................................................................................. 134

VII

List of Figures Figure 1 Location of North and South Nandi forests of Kenya .................................................. 16 Figure 2. The mean monthly rainfall distribution of Nandi South ............................................18 Figure 3 Fragmentation of Kakamega-Nandi forest during the last hundred years ..................... 19 Figure 4 The result of excision in South Nandi Forest. Photo showing the established settlement (village and school) at Bonjoge ................................................................................................ 22 Figure 5 Layout of the quadrates .............................................................................................. 23 Figure 6. Total number of families, species and genera recorded in the Nandi Forests .............38 Figure 7 Number of species per plot in South and North Nandi Forests ....................................41 Figure 8 Species accumulation (rarefaction) curves (solid lines) and 95% confidence intervals (dashed lines) for South and North Nandi Forest. ......................................................................42 Figure 9 Dendrogram of the cluster analysis result of species abundance data of Nandi Forests. .................................................................................................................................................47 Figure 10 Ordination based on Detrended Correspondence Analysis (DCA) with abundance of species from Nandi Forests. ......................................................................................................51 Figure 11 Species diversity according to growth form in Nandi Forests (a) and North and South Nandi Forests separately (b) .....................................................................................................66 Figure 12 Height class distributions of woody plant species in Nandi Forests (a) and South and North Nandi Forests (b). ...........................................................................................................67 Figure 13 Diameter class frequency distribution of woody plants in Nandi forests (a) and in North and South Nandi Forests (b) ........................................................................................... 68 Figure 14 Different diameter class frequency distribution patterns for selected tree species in Nandi Forests ........................................................................................................................... 70 Figure 15 Mean basal area per ha of South and North Nandi forests. ........................................72 Figure 16 Mean number of seedlings per plot in South and North Nandi Forests ...................... 83 Figure 17 Relative propotion of seedlings in terms of species growth form in Nandi Forests ....84 Figure 18 Relative density of top 20 seedling rich woody plant species of North Nandi Forest. 88 Figure 19 Relative density of top ten seedling rich tree species of North Nandi Forest .............88 Figure 20 Top 20 seedling rich species in South Nandi Forest. .................................................89 Figure 21 Relative densities of seedlings of top ten seedling rich tree species in South Nandi Forest. ......................................................................................................................................90 Figure 22 Seedling species accumulation (rarefaction) curves (solid lines) and 95% confidence intervals (dashed lines) for South and North Nandi forests ........................................................ 91

VIII

Figure 23 Ordination based on Detrended Correspondence Analysis (DCA) with abundance of woody plant species seedlings from Nandi Forests. ..................................................................93 Figure 24 Mean number of sprout (shoot) per stump in stump diameter classes ..................... 101 Figure 25 Regression analyses of stump diameter on the number of sprouts/stump of three species following cutting, and tree and/or branch fall disturbances in Nandi Forests ............... 102 Figure 26 Total number of stumps and number of sprouted stumps vs stump height class ....... 103 Figure 27 Location of Kobujoi (black circle) and Bonjoge (white circle) ................................ 113 Figure 28 Number of Taxa recorded in the study quadrates at Kobujoi and Bonjoge .............. 116 Figure 29 Mean number of species per plot per study site of South Nandi Forest ................... 118 Figure 30. Species accumulation (rarefaction) curves (solid lines) and 95% confidence intervals (dashed lines) of Kobujoi and Bonjoge (South Nandi forest)................................................... 119 Figure 31 Species proportion in terms of growth forms at Kobujoi and Bonjoge. .................... 121 Figure 32 Height class distributions of woody plant species at Kobujoi and Bonjoge ............. 122 Figure 33 Diameter class frequency distribution of woody plants at Kobujoi and Bonjoge ...... 122 Figure 34 Diameter class frequency distribution of selected tree species at Kobujoi and Bonjoge ............................................................................................................................................... 124 Figure 35 Mean basal area (m2 per ha) of Nandi forest at Kobujoi and Bonjoge ..................... 126 Figure 36 Mean number of seedlings per plot (45 m2) at Kobujoi and Bonjoge ....................... 129 Figure 37 Relative propotion of seedlings in terms of species growth form at Kobujoi and Bonjoge ................................................................................................................................. 130 Figure 38 Relative density of top 15 seedling rich woody plant species at Kobujoi (a) and Bonjoge (b) of South Nandi forest. ......................................................................................... 131

IX

Abstract Nandi forests (South and North Nandi forests) are situated in the Rift Valley Province of Kenya very close to Kakamega forest. From previous documents it has been seen that Kakamega and Nandi forests were connected to each other forming one big „U‟ shaped forest block till the beginnings of 1900s. Due to human pressures, currently there are three different forests form the previous one block forest. Although they were one forest, information on Nandi forests is very scanty when it is compared to that of Kakamega forest. The species composition and diversity as well as plant communities and population structure of Nandi forests have not been studied. Information is not available about the similarity status of South and North Nandi forests. Furthermore the natural regeneration potential (seedling bank) of these forests is not well studied and documented. Hence this study aims to fill these gaps.

In this study totally 76 quadrates (49 from South Nandi and 27 from North Nandi) were used to collect data. In the South Nandi forests 27 of the quadrates were laid in the better side of the forest (at Kobujoi) and the remaining 22 were in the heavily disturbed part of this forest (Bonjoge). The quadrates were arranged on transects that have one to one and half km which were parallel to the slope. The distance between the quadrates was 100 meter and transects are 500 m apart. The size of the main quadrate was 400 m2 (20 X 20 m) which also had five small plots (3 X 3 m) distributed on the four corners and in the center. Each woody plants (climbers, shrubs and trees) having more than one meter and greater than two centimeter diameter at breast height (dbh) were measured and recorded. Seedlings and herbaceous plants were sampled in the smaller plots. Individual plants were identified at species level and when it was not possible to identify in the field voucher specimen were prepared and latter identified at the East African Herbarium, National Museum of Kenya, and Nairobi. Clustering and ordination were performed using PC-ORD and CANOCO ecological softwares, respectively. For both clustering and ordination abundance data of the species was used. Shannon diversity index and evenness were computed using PC-ORD while similarity indices, Fisher alpha, rarefaction, species richness estimation (nonparametric species richness estimators) were conducted using EstimateS. Indicator species analysis was undertaken using PC-ORD. Basal area and height class distribution at forests level or site level (Bonjoge and Kobujoi) and diameter (dbh) class distribution for selected trees species were performed to evaluate population structure. Furthermore importance value (IV) of woody plant species was calculated. SPSS version 16 was used to undertake both parametric (when data assume normal distribution) and nonparametric X

(when data are not assuming normal distribution) comparison of means, correlation and regression analysis.

In this study totally 321 vascular plant species comprising 92 families and 243 genera were identified in Nandi forests (both South and North Nandi forests). In South Nandi forest 253 plant species form 82 families and 201 genera were recorded while in North Nandi 181 species comprising 67 families and 155 genera were recorded. Jackknife second order estimators gave the highest species richness estimate for both South and North Nandi forests i.e. 284 and 209, respectively. In the case of highly disturbed and less disturbed parts of South Nandi forest 138 and 172 vascular plant species were recorded, respectively. Asteraceae, Rubiaceae and Euphorbiaceae are the top three species rich families of Nandi forests. In terms of different diversity measures (i.e. alpha and beta diversity, Fisher alpha, Shannon diversity and evenness indices) South Nandi is more diverse than North Nandi forest. Sørensen and Jaccard (classic) as well as their respective abundance based similarities showed that there is a low species similarity between South and Nandi forests. The cluster analysis resulted in three different plant communities and this result is supported by the ordination result. South and North Nandi forest has inverted „J‟ height class distribution showing that larger proportion of woody plant individuals are found in the lower height classes. Similar pattern is observed when the diameters of all woody plants were considered together. However, different diameter class distributions (seven types) were identified when selected tree species were analyzed separately. It has been observed that the basal area of South Nandi forest is significantly lower than that of North Nandi forest (Mann-Whitney U =358, p < 0.001). Similarly Bonjoge has significantly lower basal area (t-value=3.77, p